1. Field of the Invention
The invention relates to a method of continuously extracting magnesium and to a multiple-cell flow apparatus in the processing line for continuously extracting magnesium, particularly by electrolysis.
Continuous methods of extracting magnesium are presently among the most promising trends in promoting further improvements in electrolytic extraction of magnesium.
2. Description of the Prior Art
Known in the art is a method of continuously extracting magnesium by subjecting chloride electrolytes to electrolysis (USSR Inventor's Certificate No. 257,059). The '059 method comprises the steps of adding magnesium chloride to the electrolyte, refining the electrolyte, introducing the resultant electrolyte to a bank of electrolysis cells series-connected by conduits, feeding the electrolyte with the magnesium extracted in the electrolysis cells to separate the magnesium from the electrolyte, accumulating the magnesium and withdrawing the same from the process as well as feeding depleted electrolyte to add magnesium chloride thereto.
As used herein "an electrolyte enriched in magnesium chloride" is an electrolyte containing from 30 to 50% by weight magnesium chloride. As used herein "a recycled electrolyte" is an electrolyte that is passed through a bank of electrolysis cells series-connected by conduits and containing from 16 to 20% by weight magnesium chloride at the inlet side of the first electrolysis cell of the bank and from 8 to 12% by weight magnesium chloride at the outlet side of the last cell. In practice, the aforementioned method will make it possible to centrally prepare the starting materials for the electrolysis, to substantially reduce the scope of maintainance of the electrolysis cells, and to enhance labor efficiency, and to improve working conditions.
The prior-art method contemplates concentration of the whole amount of the recycled electrolyte, that has undergone the electrolytic treatment, in the electrolysis cells, whereby the flow of the enriched electrolyte passed to be refined is increased and the degree of refining the electrolyte supplied to the bank of the electrolysis cells is reduced. Since the enriched electrolyte is of an inferior quality, the processing characteristics of the electrolytic cells will also be an inferior quality, such as current efficiency, specific current consumption, etc. In addition, mixing of the material containing an appreciable amount of magnesium chloride (around 100%) with the recycled electrolyte is accompanied by a high heat evolution which is due to exothermic reactions occuring when magnesium chloride comes in contact with the components of the recycled electrolyte such as sodium chloride and potash chloride. This leads to overheating of the electrolyte supplied to the bank of the electrolysis cells and hence to disturbances in performance of the electrolysis cells. Also, heating of the recycled electrolyte containing the magnesium extracted in the electrolytic cells is required to improve conditions for the separation of the magnesium from the recycled electrolyte and to get a more refined magnesium to be withdrawn from the process, which increases power consumption per unit end product.
The prior art also teaches a method of the continuous electro-winning of magnesium (USSR Inventor's Certificate No. 259,401) which comprises the steps of enriching an electrolyte in magnesium chloride, refining the electrolyte, feeding the resultant electrolyte to a bank of electrolytic cells series-connected by conduits, carrying the electrolyte containing the magnesium in the electrolytic cells, separating the magnesium from the electrolyte, accumulating the magnesium and withdrawing the same from the process and delivering the electrolyte to add magnesium chloride, the flow of the recycled electrolyte following the step of separating the magnesium being divided into several flows of which one is delivered to be enriched in magnesium chloride and the rest are added to the electrolyte enriched in magnesium chloride following the step of its refining.
The above-described method permits the flow of the concentrated electrolyte, that is fed for refining, to be decreased and hence to improve the quality of the electrolyte supplied to the electrolytic cells.
However, the problems of the exothermic heat, current consumption and the optimum performance of the electrolytic cells is to be solved.
The above method may be practiced in a processing line comprising electrolytic cells connected by conduits to perform the steps of enriching the electrolyte in magnesium chloride, separating magnesium from the electrolyte, refining the electrolyte and dividing the same into several flows. Yet a single multiple-cells flow apparatus as disclosed in USSR Inventor's Certificate No. 487,287 is believed to be more suitable for carrying out the steps of enriching the electrolyte in magnesium chloride, separating magnesium from the electrolyte, and dividing the electrolyte into several flows. The apparatus comprises a chamber for separating magnesium from the electrolyte, a chamber for enriching the electrolyte in magnesium chloride, and a chamber for dividing the electrolyte into two or more flows. The chambers are separated by walls. In the apparatus the chamber for enriching the electrolyte in magnesium chloride is disposed between the chamber for separating magnesium from the electrolyte and the chamber for dividing the electrolyte into flows. The walls separating the chambers are provided with overflow passages through which the electrolyte flows from one chamber into another. The above apparatus as utilized in practicing the above method will make for a considerable reduction in the length of conduits and save labor.
However, there is still a need for heating of the electrolyte to 670.degree. to 720.degree. C. in the chamber for separating magnesium from the electrolyte in order to maintain optimum conditions therein, namely skull prevention and complete magnesium separation. Such heating entails extra power consumption and a respective high power consumption per unit end product. The temperature of the recycled electrolyte is still high (750.degree.-770.degree. C.).